Just go to Lowe's. They stock Korky parts for Toto. The boxes are plainly labeled so it's quite simple. A constantly running toilet is often a flapper issue, so first, you might check to see if yours is seating right. It could be snagging on the chain or maybe not lined up correctly.

If it's running, there are two possible reasons. One might be that the fill valve is stuck. This isn't usually the case. The other is that the fill valve is fine but water is draining from the tank and the fill valve is just trying to keep the tank full. That's more likely the case. The way to differentiate is to look in the tank. Look at the overflow riser, which is the pipe that comes up from the flush valve at the bottom of the tank. Is water running over the top of that riser, or is it below there? If below, then it's most likely a flapper issue.

On a flapper issue, it may just be worn out and need to be replaced. Or it may be fine and just not seating properly. Take a look. If everything in the tank looks fine, and it opens and attempts to close cleanly into the hole and just doesn't seal, then you can replace it. Best option: the Korky 3060BP 3" adjustable flapper.

Good luck, and let us know how it goes. (If it does turn out to be a fill valve issue, you can often just replace the cap R528 and fix it for like $3. If you want to replace the whole valve, get the Korky MaxPerformance 528MP (528MPK at Lowe's). The 528T you linked to is good for the original Drake, but will overfill the bowl on the Drake II. You want the 528MP, which is infinitely-adjustable, and cheaper than the 528T, usually.) If it does turn out to be a fill valve replacement issue, come back and I'll point you to a Korky video on how to replace it.

You don't normally need to replace the whole valve...the cap is the easy thing that makes the seal. There could be some sand or other debris caught in there, and just taking it out, cleaning it off, and reinstalling it may solve the problem. The instructions on how to replace the cap are on the package - it's a couple of minute affair, and no tools are required. If you really want to replace the whole valve, that's a little more involved, but still easy.

Actually, to get TOTO Stock Fill valves or flapper parts, I recommend this website. This website is owned by TOTO. Hopefully you find what part your looking for https://totostore.us.com/Default.aspx

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Sure! Pay them $30 for a TSU99A.X fill valve when you can buy a virtually-identical Korky 528MP at Lowe's for $10.47. It won't have the little gauge that lets you set the refill percentage to exact factory specs (you'll have to eyeball it), and it won't have the chart that shows you how many pegs tall to make the valve (again, you'll have to eyeball it), but otherwise, I-dentical.

And if you want that THU331S flapper for your Ultramax II or Drake I, it's out of stock even though they get $21 for it. Fortunately, you could pick up the (identical, because Korky makes both) Korky 2021BP flapper at walmart online for $9.88, or the Korky universal adjustable 3" flapper at Lowe's for like $11.

Don't get me wrong: the Toto customer service folks are great. And if you need something unusual, they're your cats. But the great thing about Totos is that generally they accept industry-standard, readily-available parts you can get almost anywhere.

AS Toilet -- get it in Big Box Store, but they don't have the AS Parts.
Toto Toilet -- can't get it in Big Box Store, but the Big Box and your local hardware store probably carry the common parts.
Delta Toilet -- get it at HD, but you can only get the parts (including the unique 3-3/4" flapper) ONLINE from HD, and -- oh, snap! -- it's out of stock. Sorry your toilet is running. And the fill valve costs $38.75 and is only available online from HD.

AS Toilet -- get it in Big Box Store, but they don't have the AS Parts.

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Need more detail on that statement. My AS Cadet 3 uses Fluid Master made parts. For instance, the OEM flush valve overflow tube is solid or non-adjustable. You can purchase a adjustable version at HD. Both OEM and HD sold version have the adjustable flapper valve.

Need more detail on that statement. My AS Cadet 3 uses Fluid Master made parts. For instance, the OEM flush valve overflow tube is solid or non-adjustable. You can purchase a adjustable version at HD. Both OEM and HD sold version have the adjustable flapper valve.

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I hear you, so far as it goes, but...

If I bought a Champion 4 and that stupid flush funnel cracked when I was trying to replace the finicky rubber seal, I could just buy the (fluidmaster-made) funnel at HD? I think not.

Of course, I could replace it with the new Korky 3 inch flush valve and flapper kit and be done with it, but that sort of defeats the purpose of buying the Champion in the first place.